I agree wholeheartedly with the premise that this couple probably did not realize the disconnect in their own marriage until their experience with you. If their other experiences were relatively less intense, then they may have perceived themselves as being really tight. Now they know it could be better.
It could very well be that given time, they will return and things will be even better.
As for the changes you made in your personality to learn and adapt to poly, they are not tied to the couple. They are a part of you and will remain, even if instead you all move on.
I understand your grief. I imagine many of us do.